Physics 2B, Electricity and Magnetim -- Winter 2009 Instructor: B. Grinstein
Quiz # 4
INSTRUCTIONS: Fill, tear and return the bottom strip of the front page with your scantron. Keep the top portion of the
front page and the rest of the quiz. Use a pencil #2 to fill your scantron. Write your code number and bubble it in under
"EXAM NUMBER". Bubble in the quiz form (see letter A--D at bottom of page) in your scantron under "TEST FORM"
Useful numbers: K = 9.0 109 Nm2 /C2 , o = 8.85 10-12 C2 /Nm2 , e = 1.60 10-19 C, me = 9.11 10-31 kg
µo = 4 10-7 T m/A
1) The figure shows an electric field in space:
Which of the following electric potential graphs best dercribes this field?
A)
B)
C)
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quiz version A-1
D)
E)
2) In the circuit shown in the figure the capacitance C1 is twice as large as the capacitance C2. Initially, the
switch has been in position A for a long time.
The switch is then flipped to position B. A long time after the swicthed is flipped, the charge in the
capacitor C2
A) is zero
B) is equal to the charge in capacitor C1
C) is half the charge in capacitor C1
D) is twice the charge in capacitor C1
E) none of the above
3) The figure bellow shows a contour map of electric potential.
Estimate the electric field strength at point 2
A) 10 V/m
B) 5 V/m
C) 8.6 V/m
quiz version A-2
D) 0 V/m
E) 20 V/m
4) The figure bellow shows a contour map of electric potential.
Rank order from smallest to largest, the magnitudes fo the electric field Ea through Ed at the four indicated
points.
A) Eb = Ed < Ea = Ec
B) Ed < Ea = Ec < Eb
C) Eb < Ea = Ec < Ed
D) Eb = Ed < Ea < Ec
E) Ea = Ec < Eb = Ed
5) In the circuit shown in the figure the capacitors are initially uncharged. The switch is first thrown to position
A, remians there for a long time, and then it is thrown to position B. Let the charges on the capacitors be Q1,
Q2, and Q3 and the potential difference across them be V1, V2 and V3. With the switch having been in
position B for a long time, which of the following relations is correct? (Sign convention for the potential
differences V1, V2 and V3: take them as the difference between the upper and lower plates as drawn in the
figure above).
A) Q1 + Q2 = Q3
B) V1 + V2 = V3
C) Q1 = Q2 = Q3
D) V3 = V0
E) V1 = V2 = V3
quiz version A-3
6) Three capacitors are arranged as shown. C1 has a capacitance of 5.0 pF, C2 has a capacitance of 10.0 pF,
and C3 has a capacitance of 15.0 pF. If the voltage drop across C2 is 175.0 V, the voltage drop across the
entire arrangement is colsest to
A) 1100 V
B) 320 V
C) 700 V
D) 290 V
7) Two parallel circular plates with radius 4.0 mm carrying equal-magnitude surface charge densities of
±2.0 µC/m2 are separated by a distance of 2.0 mm. How much stored energy do the plates have?
A) 71 nJ
B) 2.3 nJ
C) 23 nJ
D) 7.2 nJ
8) The electric potential V in a region of space is given at a point P a distance r from the origin and at an
angle above the x axis by the expression V = A r 5 cos sin 2, where A is a numerical constant with
dimensions of volts/meter 5. The x-component of the electric field at point P is
A) 5A r 4 sin 2
sin 2 (1+2cos2)
C) -5A r 4 sin 2
D) -2A r 4 sin cos
E) -A r 4 sin 2
B) -A r 4
quiz version A-4
Answer Key
Testname: QZ4
1) A
2) C
3) E
4) D
5) B
6) A
7) C
8) B
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Name________________________________________
Quiz ID_________________________
quiz version A-5